The best cue is to keep your shoulder blades back and down. The first few reps show the incorrect position. In the last few reps, the shoulder are back and down.
For any horizontal pulling exercise, like seated cable rows, keeping the shoulders back and down will ensure your lats and mid back are being hit the hardest, instead of just the upper traps and biceps.
In the video, the first couple of reps are performed incorrectly and the last couple of reps are performed with the shoulders back and down.
This six-week program breaks some of the currently accepted rules for workout volume and duration. That's why you'll do more than 20 sets per workout and you'll train for 60 to 75 minutes.